7,416 research outputs found
FOCIS: A forest classification and inventory system using LANDSAT and digital terrain data
Accurate, cost-effective stratification of forest vegetation and timber inventory is the primary goal of a Forest Classification and Inventory System (FOCIS). Conventional timber stratification using photointerpretation can be time-consuming, costly, and inconsistent from analyst to analyst. FOCIS was designed to overcome these problems by using machine processing techniques to extract and process tonal, textural, and terrain information from registered LANDSAT multispectral and digital terrain data. Comparison of samples from timber strata identified by conventional procedures showed that both have about the same potential to reduce the variance of timber volume estimates over simple random sampling
Cosmic Rays: The Second Knee and Beyond
We conduct a review of experimental results on Ultra-High Energy Cosmic Rays
(UHECR's) including measurements of the features of the spectrum, the
composition of the primary particle flux and the search for anisotropy in event
arrival direction. We find that while there is a general consensus on the
features in the spectrum -- the Second Knee, the Ankle, and (to a lesser
extent) the GZK Cutoff -- there is little consensus on the composition of the
primaries that accompany these features. This lack of consensus on the
composition makes interpretation of the agreed upon features problematic. There
is also little direct evidence about potential sources of UHECRs, as early
reports of arrival direction anisotropies have not been confirmed in
independent measurements.Comment: 46 pages, 30 figures. Topical Review to appear in J. Physics
Information criteria for astrophysical model selection
Model selection is the problem of distinguishing competing models, perhaps
featuring different numbers of parameters. The statistics literature contains
two distinct sets of tools, those based on information theory such as the
Akaike Information Criterion (AIC), and those on Bayesian inference such as the
Bayesian evidence and Bayesian Information Criterion (BIC). The Deviance
Information Criterion combines ideas from both heritages; it is readily
computed from Monte Carlo posterior samples and, unlike the AIC and BIC, allows
for parameter degeneracy. I describe the properties of the information
criteria, and as an example compute them from WMAP3 data for several
cosmological models. I find that at present the information theory and Bayesian
approaches give significantly different conclusions from that data.Comment: 5 pages, no figures. Update to match version accepted by MNRAS
Letters. Extra references, minor changes to discussion, no change to
conclusion
The Curious Case of Lyman Alpha Emitters: Growing Younger from z ~ 3 to z ~ 2?
Lyman Alpha Emitting (LAE) galaxies are thought to be progenitors of
present-day L* galaxies. Clustering analyses have suggested that LAEs at z ~ 3
might evolve into LAEs at z ~ 2, but it is unclear whether the physical nature
of these galaxies is compatible with this hypothesis. Several groups have
investigated the properties of LAEs using spectral energy distribution (SED)
fitting, but direct comparison of their results is complicated by
inconsistencies in the treatment of the data and in the assumptions made in
modeling the stellar populations, which are degenerate with the effects of
galaxy evolution. By using the same data analysis pipeline and SED fitting
software on two stacked samples of LAEs at z = 3.1 and z = 2.1, and by
eliminating several systematic uncertainties that might cause a discrepancy, we
determine that the physical properties of these two samples of galaxies are
dramatically different. LAEs at z = 3.1 are found to be old (age ~ 1 Gyr) and
metal-poor (Z < 0.2 Z_Sun), while LAEs at z = 2.1 appear to be young (age ~ 50
Myr) and metal-rich (Z > Z_Sun). The difference in the observed stellar ages
makes it very unlikely that z = 3.1 LAEs evolve directly into z = 2.1 LAEs.
Larger samples of galaxies, studies of individual objects and spectroscopic
measurements of metallicity at these redshifts are needed to confirm this
picture, which is difficult to reconcile with the effects of 1 Gyr of
cosmological evolution.Comment: Minor revision, accepted for publication in ApJ
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